Polyphenol Composition in the Ripe Fruits of Fragaria Species and Transcriptional Analyses of Key Genes in the Pathway

Abstract

Polyphenolics are important secondary metabolites in strawberry as they fulfill a wide variety of physiological functions and are beneficial to human health. Seventeen structurally well-defined phenolic compounds including phenylpropanoids, flavonols, flavan-3-ols, and anthocyanins were individually analyzed by LC-MS in the ripe fruits of two cultivars of the commercial strawberry (Fragaria × ananassa Duch., Rosaceae) as well as in accessions of F. vesca, F. moschata, and F. chiloensis. Metabolic analysis revealed that the majority of the compounds analyzed accumulated in a genotype-dependent manner. Transcriptional studies of genes encoding for enzymes of the biosynthetic pathway such as phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, chalcone synthase, and flavonoid 3'-hydroxylase could partially explain the different levels of polyphenolics observed in the Fragaria species. The results can provide a sound basis for selecting markers for the development of cultivars with high phenolic content, which can be of value for the food industry.

Effect of ethylene treatment on phytochemical and ethylene-related gene expression during ripening in strawberry fruit Fragaria x ananassa cv. Camino Real

“…Strawberries are a source of phenolic compounds such as flavonoids, phenolic acid derivatives, and anthocyanins, which are all synthesized by the phenylpropanoid pathway (Muñoz et al, 2011), in which phenylalanine ammonialyase (PAL) is the key enzyme (Singh et al, 2010). A slight increase in the anthocyanin content in postharvest red fruits treated with ethephon was observed.…”

“…However, Villarreal et al (2010) observed a significant increase in PAL activity and a decrease in the phenolic content during the ripening of white strawberries treated with ethephon, indicating that a direct correlation is lacking. However, molecular analyzes of the strawberry cultivar Camarosa during ripening led Muñoz et al (2011) to observe higher PAL expression levels in green and red fruit compared to white. These data suggest that differences in the level of anthocyanins and phenolic compounds across stages in the present study may be related to PAL activity.…”

Pigments in Strawberry

“…This minor pigment is responsible for the dark red colors. Pelargonidin-3-rutinoside can also be commonly found in a much smaller proportion in cultivars like "Camarosa" or "Parker," but this molecule is absent from native species like the diploid F. vesca or octoploid F. chiloensis [2,15]. Other anthocyanins have been identified in other cultivars.…”

“…The same study noted that the fruits showed low levels of CHS, DFR, and F3H, leading to the compelling hypothesis that the allergen was related to pigment synthesis. To test the direct association, Munoz et al (2011) used the agro-infiltration protocol to suppress the allergen in developing fruits [15]. The results show that Fra a suppression leads to decreases in pigmentation, and leads to the speculation that the protein may be required in the transportation of substrates between flavonoid pathway enzymes.…”

“…They contribute to fruit coloration by stabilizing the unstable anthocyanin chromophore [11]. In most cases, the most common flavonols found in strawberry fruit are kaempferol-3-O-glucoside and quercetin-3-O-glucoside with a higher amount of kaempferol glucoside especially in Fragaria × ananassa cv "Camarosa" and "Parker" [15]. Glucuronide conjugates can also be found bound with kaempferol and quercetin aglycones.…”